fix(ocr): round-5 review nits — empty-pages failure, comments, test cleanup

Round 5 review (PR #910), all nits, no blockers:
- _result_from_success: a succeeded job with `pages=[]` (empty list, not just a
  missing key) is now a per-document failure ("no pages returned") instead of a
  silent 0-chunk success. Test added.
- Comment the deadline-expiry path: the gateway-side job isn't cancelled (no
  cancel endpoint at this layer) — it's reaped by the gateway file purge; we just
  stop polling it.
- Drop the vestigial status="pending" from the BatchOcrJob test fakes (the column
  was removed in round 4; BatchPollResult.status fakes are untouched).

1653 unit tests pass; ruff + ty green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/embedding/gateway_batch_client.py

@@ -184,8 +184,13 @@ def _result_from_success(body: dict[str, Any]) -> BatchPollResult:
             error="batch job succeeded but returned no results",
         )
     item = results[0]
-    if item.get("error") is not None or item.get("pages") is None:
-        return BatchPollResult(status=_FAILED, pages=[], error=item.get("error"))
+    # ``not item.get("pages")`` catches both a missing key AND an empty list:
+    # a succeeded job that produced zero pages is a per-document failure (nothing
+    # to index), not a silent 0-chunk success.
+    if item.get("error") is not None or not item.get("pages"):
+        return BatchPollResult(
+            status=_FAILED, pages=[], error=item.get("error") or "no pages returned"
+        )
     # Defensive on both fields (the page index falls back to position) so a
     # malformed page object degrades rather than raising KeyError mid-parse.
     pages = [